For my blog post this week I am supplying some comments on the paper entitled Noncontact Tactile Display Based on Radiation Pressure of Airborne Ultrasound by Takayuki Hoshi, Masafumi Takahashi, Kei Nakatsuma, and Hiroyuku Shinoda. In their paper they present some results from a holographic system that incorporates ultrasound to provide tactile feedback.

It was not clear to me what sort of pulses could be generated by the ultrasound emitter. The examples of the raindrops falling and the elephant walking swiftly across the user’s palm seemed to only require short pulses of ultrasound. Could a sustained pressure be exerted (if for example the elephant stood still)? Would the experience of a continuous pressure seem less realistic than the short pulses?

The paper pointed out problematic areas with the current setup. First, the users must wear a marker on the tip of their finger to allow hand tracking (though this is far superior to many alternatives as discussed below). There is also the problem of the user’s hand getting in the way of the projection of the holographic image (this is not a problem with the tactile ultrasound emissions, just the holography). Ultrasound emissions can be damaging to human subjects in two ways: first, the emissions can damage skin tissue, limiting the strength of the signals that can be used. Second, the signals may damage ears, so users are required to wear ear protection. Also, the ultrasound emitter is loud, which detracts from the user experience.

Despite the drawbacks it seemed clear that ultrasound was preferable in many respects to alternative approaches. Other approaches include wearing gloves with stimulators adjacent to the skin at all times, using robotic arms, or wearing thin membranes while submerged in water.

This setup does give users the sensation of physically interacting with an object, unlike the Microsoft Kinect. It seems to me this rings truer with our experience of the world. Even when we are typing on a keyboard the world pushes back on us.

At the far end of the spectrum is a setup like the holodecks of Star Trek: complete immersion in a holographic world which admits of interaction. Is equipping a room size space with ultrasound emitters feasible? Or would the blasts of ultrasound from all walls disorient the user, break their eardrums, and damage their skin?